Theoretical and experimental studies will be devoted to the question of whether or not a model of human gait is realistic in which the muscles of the swing leg are silent after the end of the double support phase. The studies will examine both normal and pathological gaits at both fast and slow speeds. Pathological gaits addressed will include Trendelenburg, gluteus maximus, ankylosis of the knee, instability of the knee, equinus, spastic plantar flexion of the ankle, and dropfoot in paralysis or muscular weakness. The predictions of the model, to be tested against new and existing experimental and clinical observations, will allow a simple criterion to be established within each gait pathology, marking the boundary between mild and severe handicaps to progression.